This grant is a continuation of our ongoing studies on mechanisms of irritant induced lung injury. It is based on several novel observations made by our laboratory that have led us to conclude that alveolar and interstitial macrophages, as well as Type II aIveolar epithelial cells, are critical cellular mediators of lung damage. Using ozone as a model irritant, we have discovered that these cells are "activated" to produce a cascade of cytokines and cytotoxic mediators including nitric oxide, hydrogen peroxide, interleukin-1 and tumor necrosis factor-alpha, which have the capacity to directly induce tissue injury and/or amplify the inflammatory response. We also discovered that ozone exposure induces upregulation and functional activation of receptors for the proinflammatory cytokine, platelet activating factor, on alveolar macrophages. We speculate that this represents an important mechanism by which these cells become activated and contribute to tissue injury. The overall objective of our studies is to analyze the role of inflammatory mediators derived from lung macrophages and Type II cells in lung injury induced by acute as well as subchronic exposure of rats to ozone. In situ localization techniques will be used to determine if lung macrophages and Type II cells are "activated" in vivo following ozone exposure to produce cytotoxic and proinflammatory mediators and to express functionally active cytokine receptors. We will also evaluate the effects of modifying macrophage functioning and mediator production on ozone-induced lung toxicity. The mechanisms by which activated alveolar and interstitial macrophages contribute to the pathogenesis of tissue injury will also be examined. This will include analysis of the role of inflammatory mediators and cytokines in alveolar epithelial cell growth, differentiation and cytotoxicity. Finally, we will examine the role of collagen degradation fragments which are generated following ozone induced lung injury in activation of lung macrophages and Type II cells. The results of these studies should provide important mechanistic insights into the role of macrophages and epithelial cells in lung injury, and potential new approaches for pharmacologically abrogating acute lung injury induced by inhaled irritants.